we learned good sit stay while eating meals... Che would sit stay position when I hold his food bowl, great motivator.... initially I just stand in front of him, then introduce distance, then "find it" command...
with sit try using it in everyday life- watch you pups, every time they sit on their own- click and treat, it might require spending quite a lot of time watching them and carrying clicker on key chain but it is well worth it.
I would also hand feed your pups for couple of weeks, first in static position, one piece of kibble after another, later by walking/ moving your hands- what you need to achieve is for them to pay attentions to your hands and know that good things coming out of it.
I would not worry about luring Fluff into sit, once you KNOW that she knows what you want from her and she does sit reliably to the luring verbal and hand command THEN you can start fading the lure and ask for the sit by first holding the treat at your side then by holding cookie jar then by standing at the shelf with cookie jar etc... you can only move to the next stage once you KNOW your dog understands and knows what are you asking him/ her to do...
I am also finding that Che and Sammy are different in the learning methods... for Che it takes next to nothing, he is so good at reading my body language and hand movement that I could introduce verbal command at same time with hand signal and he gets it right away and I could pretty much lure him into anything with good piece of food, with Sammy I need lots of small steps and that is where clicker is very rewarding- if she only moves her head or ear in right direction she gets rewarded, then a step, then another, sometimes you need to feed as a machine gun style for any small step in right direction, she gets it but it is much slower process...